This invention relates to intravascular catheters that have means for reducing stenosis and thrombosis at the tip of the catheter.
The treatment of a number of medical conditions requires the placement of catheters within a patient""s blood vessel for an extended period of time. These long-term applications include blood access for hemodialysis, chemotherapy, parental nutrition, blood transfusions and blood sampling.
Vascular access with catheters was first introduced more than 20 years ago. With the advent of soft, flexible silicone double lumen catheters, both acute and chronic hemodialysis became a routine procedure. Although subclavian dialysis catheters are easily inserted and well tolerated, catheter lifespan averages about three months. This is of great concern to patients on maintenance dialysis.
It is well known in the medical field that chronic placement of a catheter in a patient""s blood vessel often results in catheter failure due to aspiration of the blood vessel wall into the tip of the catheter, clot or thrombus formation at the tip of the catheter, or stenosis around the tip of the catheter. A catheter failure resulting from one or more of these mechanisms is evidenced by an inability to aspirate and/or infuse fluid through the catheter, generally referred to as catheter occlusion. Typically, catheter occlusions caused by aspiration of the blood vessel wall or clot formation at the catheter tip may be resolved by repositioning the catheter tip or infusing antithrombotic agents.
Stenosis is a narrowing of the blood vessel lumen as seen in a venogram and, in general, can be due to either the formation of a thrombus within the blood vessel or a thickening of the blood vessel wall. The generally accepted view is that stenosis around the tip of a catheter implanted within a blood vessel is due to the formation of a thrombus resulting from a biochemical reaction to the introduction of a foreign material into the blood vessel. Previous attempts to prevent catheter occlusion have centered around thromboresistant coatings on the catheter surface in order to prevent the biochemical reaction of the patient""s blood to the material of which the catheter is formed.
Prior art related to the present invention deals with the placement of stents within a diseased blood vessel to treat the problems associated with stenosis. Stents range from simple wire meshes used in U.S. Pat. No. 4,800,882, to a canister made of hydrophilic plastic which expands upon placement in a blood vessel as in U.S. Pat. No. 4,434,797. Stents are typically secured to a deployment catheter for insertion into the patient""s blood vessel via a percutaneous procedure. Surgical placement of these stents is achieved by feeding the catheter from a distant site, e.g., a percutaneous puncture into the femoral artery, to the stenosis target. The deployment catheter is then removed, leaving the stent within the blood vessel lumen.
Prior publications on the subject of mounting devices in the blood stream include xe2x80x9cRegistration of Phoric Changes of Blood Flow by Means of a Catheter-Type Flowmeter,xe2x80x9d by Heinz Pieper printed in The Review of Scientific Instrument 29(11):965-967, November 1958, and U.S. Pat. Nos. 4,425,908; 4,936,823; 4,813,930; 5,135,517; and 4,654,028. However, none of these address and solve the problems presented in the field of the present invention.
The present invention is directed to an intravascular catheter that has means to retain the tip of the catheter within a blood vessel lumen such that the tip of the catheter is prevented from contacting the wall of the blood vessel. This prevents repeated impact between the catheter tip and blood vessel wall. This reduces denudation and damage to the endothelial and smooth muscle cells that line the blood vessel wall. By reducing damage to these cells, the invention allows for the cells to continue to release the bioactive molecules that normally prevent and reverse the thrombotic and coagulation processes in blood.
Most vascular injury research is in the area of arterial injury; however, the mechanism that regulates cellular growth in injured veins is not known. It is a reasonable assumption that the xe2x80x9cresponse to injury hypothesesxe2x80x9d proposed in Ross, R., Glomset, J. A., xe2x80x9cThe Pathogenesis of Atherosclerosis,xe2x80x9d N. Engl. J. Med. 295:369-77, 1976, can also be applied to injuries in the venous system. This hypothesis is based on the following observations after injury to the lumen of the blood vessel: (1) platelet adherence and degranulation precedes smooth muscle cell proliferation; (2) intimal thickening in injured arteries of thrombocytopenic animals is reduced; (3) platelet granules contain potent mitogens for cultured smooth muscle cells. Based upon these observations, Ross and Glomset suggested that a high local concentration of growth factors, particularly platelet-derived growth factors released from degranulating platelets could stimulate smooth muscle cell proliferation. Their hypothesis is based on a relationship between the thrombosis that occurs within an injured vessel and the subsequent cell growth associated with repair of the injured vessel wall.
Normally, hemostasis results from a delicate balance between clot-stimulating and clot-inhibiting processes. Endothelial cells and smooth muscle cells in a normal blood vessel are probably the main source of clot regulating factors such as heparin or heparan sulfate. These heparin and heparin-like molecules prevent the adherence of blood proteins and platelets to the surface of a normal blood vessel. Since the endothelium is a critical component of hemostasis control, localized injury and denudation of the endothelium by repeated impact with a catheter tip results in a shift of this delicate balance toward clot and thrombus formation within a denuded region. This clot formation may occur even if the catheter is composed of a material that normally would not create a reaction in the body.
Physical damage to the wall of the blood vessel affects the release and production of a number of growth-stimulating factors such as basic fibroblast growth factor and platelet-derived growth factor. These growth factors help to overcome the antiproliferative activities of the heparan sulfates, thus helping to initiate cellular proliferation and the migration of smooth muscle cells that ultimately leads to stenosis. Therefore, preventing physical damage to the endothelial cell lining of the blood vessel wall reduced stenosis, as well as thrombosis, at the tip of the catheter.
Prior art catheters allow chronic and repeated contact between the catheter tip and the wall of the blood vessel, resulting in damage to the blood vessel as discussed previously. The tip of the catheter may repeatedly bump into different locations inside the blood vessel, or the same location a number of different times, causing a reaction, or worse, damage to the vessel wall. Further damage is caused by the aspiration of the blood vessel wall into the catheter lumen. This occurs when blood is withdrawn through the catheter, such as in the performance of dialysis.
The present invention solves the problems by approaching them from an entirely different view than the prior art attempts; namely, by preventing repeated impact between the catheter tip and the blood vessel wall. The inventor has found that repeated impact with the vessel wall and a catheter tip, even if it is a soft tip, causes a physical reaction in the blood vessel wall. This reaction occurs because of repeated contact between the catheter tip and the wall of the blood vessel even if the catheter tip is soft, and even if the tip is properly coated with antithrombotic agents. This catheter-induced reaction in the blood vessel wall may lead to the formation of a mural thrombus and/or abnormal cellular proliferation within the blood vessel wall, thus resulting in stenosis and catheter occlusion. Prior art efforts to prevent catheter occlusion through the use of thromboresistant coatings do not alleviate the physical reaction that the catheter tip may cause to the blood vessel wall by repeated impact. Therefore, chronic placement of a catheter in a patient still results in catheter occlusion in the majority of cases.
In accordance with aspects of the present invention, chronic contact between and aspiration of the blood vessel wall by the catheter tip is prevented. This reduces damage to the endothelial cells lining the blood vessel, thus reducing catheter occlusion due to stenosis and thrombosis. In addition, the occurrence of catheter occlusion resulting from aspiration of the vessel wall will be reduced.
The present invention includes, in one embodiment, an antistenotic intravascular catheter for insertion into a blood vessel. The catheter includes a tip retainer, located at the distal end of the catheter, for retaining the tip of the catheter within the blood vessel and preventing the catheter from contacting the wall of the blood vessel. The tip retainer positions the tip of the catheter within the blood vessel without substantially obstructing fluid flow through the blood vessel. The catheter also includes an internal passageway for permitting fluids to pass through the catheter. Preferably, the catheter is a double lumen catheter of the type used generally in kidney dialysis.
In all embodiments, the tip of the catheter is retained in the blood vessel by anchoring the tip with respect to the wall of the blood vessel. Advantageously, the tip retainer permits some movement of the catheter tip with respect to the vessel wall, such as slight movement forward and back or side to side with the pulsation of the blood flow. However, movement is restricted to minimize repeated contact (or all contact) of the tip with the blood vessel wall. Just as the anchor of a ship anchors a ship to the bottom but permits some movement of the ship as the water rises and falls or flows, similarly the tip retainer can be said to anchor the tip to the vessel wall but still permit some movement of the tip based on changes of the flow in which it is anchored.
Numerous alternative embodiments are disclosed for the tip retainer. In some embodiments, the tip retainer does not penetrate the wall of the blood vessel. In one embodiment, the tip retainer includes a penetrating member that does penetrate the blood vessel wall. In all embodiments, the tip of the catheter is retained in the blood vessel by anchoring the tip with respect to the wall of the blood vessel.
In one preferred embodiment, the tip retainer is two or more loops of wire that flex outward and contact the wall. The loops do not penetrate the wall tissue, but do anchor the tip in a fixed position in the blood vessel, retaining it in the blood flow and preventing contact of the tip with the vessel walls.
In another preferred embodiment, a single loop extends from the tip portion of a double lumen catheter. The single loop is composed of a flexible wire coated with silicone, silicone tubing or, alternatively, is composed of silicone tubing alone. The diameter of the loop is selected to be sufficiently large that the loop bridges any branches in the blood vessel which are likely to be encountered when the catheter is positioned within the blood vessel.
As a further alternative, the silicone tubing which forms the loop may be in fluid communication with the lumen of the catheter separate from the lumen used for the kidney dialysis. Medication can be delivered through the lumen for delivery to the walls of the blood vessel at the point of contact by the loop. This provides the distinct advantage that anticoagulant medication can be delivered specifically to walls of the blood vessel near the catheter tip.
In a further embodiment the tip retainer includes fletching to anchor the catheter tip in the blood vessel. Alternatively, the tip retainer is a plurality of single straight wires that are prestressed to flex outward or straight wires with loops on the end.
In accordance with one embodiment of the invention, the tip retainer includes penetration means for penetrating the wall of the blood vessel and preventing the tip of the catheter from moving longitudinally within the blood vessel. In this embodiment, the tip includes a loop for limiting the depth of penetration.
In one embodiment of the invention, a plurality of members run from the proximal end of the catheter to the distal end where they extend radially outward until they contact the wall of the blood vessel. In this embodiment, the catheter includes withdrawal means for withdrawing the positioning means into the catheter such that the positioning means is prevented from damaging the wall of the blood vessel when the catheter is withdrawn from the blood vessel, The withdrawal means includes a guideway that runs from the proximal end of the catheter to the distal end of the catheter. The positioning means extends from the proximal end to the distal end of the catheter within the guideway.
According to one aspect of the present invention, a method for reducing catheter failure due to stenosis or thrombosis at a catheter tip is provided. Positioning means is attached to the catheter tip, and the catheter tip and attached positioning means are placed within the blood vessel without substantially obstructing fluid flow through the blood vessel and such that the catheter tip is prevented from contacting the blood vessel wall.